<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    /* 三栏布局 */
    .three-layout {
      width: 100%;
      height: 200px;
      display: flex;
      flex-direction: row;
    }
    .three-layout .left {
      background-color: #0a0;
      height: 200px;
      width: 100px;
    }
    .three-layout .middle {
      background-color: #a00;
      height: 200px;
      flex: 1;
    }
    .three-layout .middle__item {
      width: 300px;
    }
    .three-layout .right {
      background-color: #00a;
      height: 200px;
      width: 100px;
    }
    /* 三栏布局-双飞燕 */
    .three-layout-pro {
      margin-top: 20px;
      width: 100%;
      height: 200px;
      display: flex;
      flex-direction: row;
    }
    .three-layout-pro .left {
      background-color: #0a0;
      height: 200px;
      width: 100px;
      order: -1;
    }
    .three-layout-pro .middle {
      background-color: #a00;
      height: 200px;
      flex: 1;
    }
    .three-layout-pro .middle__item {
      width: 300px;
    }
    .three-layout-pro .right {
      background-color: #00a;
      height: 200px;
      width: 100px;
    }
    /* 两栏布局 */
    .two-layout {
      margin-top: 20px;
      width: 100%;
      height: 100px;
      display: flex;
    }
    .two-layout .left {
      background-color: #0a0;
      height: 100px;
      width: 100px;
    }
    .two-layout .right {
      background-color: #a00;
      height: 100px;
      flex: 1;
    }
    
    /* 垂直居中 */
    .center-layout {
      display: flex;
      margin-top: 20px;
      border: 1px solid #aaa;
      width: 100%;
      height: 200px;
      align-items: center;
      justify-content: center;
    }
    .center-layout .center-item {
      width: 100px;
      height: 100px;
      background-color: #a00;
    }
  </style>
</head>
<body>
  <div class="three-layout">
    <div class="left"></div>
    <div class="middle">
      <div class="middle__item">
      </div>
    </div>
    <div class="right"></div>
  </div>

  <div class="three-layout-pro">
    <div class="middle">
      <div class="middle__item">
      </div>
    </div>
    <div class="left"></div>
    <div class="right"></div>
  </div>

  <div class="two-layout">
    <div class="left"></div>
    <div class="right"></div>
  </div>

  <div class="center-layout">
    <div class="center-item"></div>
  </div>
</body>
</html>